Thermal interfaces in microelectronics packages are commonly credited with a majority of the resistance for heat to escape from the chip to the attached cooling device (e.g. heat sinks, spreaders and the like). Thus, in order to minimize the thermal resistance between the heat source and cooling device, a thermally conductive paste, thermal grease or adhesive that contains thermally conductive particles is commonly used. On the chip side—(heat source) there usually exists hotspots, areas of higher power density, where most of the processing takes place, which results in a temperature gradient across the chip. These areas of higher heat and power density must be kept within a set temperature range in order for the chip to perform properly and to pass quality and specification tests at the end of manufacturing.
Control of temperature distribution has recently been addressed by changing chip design/architecture. However this requires expensive redesign of the microprocessor that may influence other operating parameters and does not address the present issues facing current high performance microprocessors. Current means to increase the heat dissipation of the microprocessor include mechanical cap standoffs in direct contact between the chip and heat sink (June et al., “Using Cap-Integral Standoffs to Reduce Chip Hot-Spot Temperatures in Electronic Packages”, 2002 Inter Society Conference on Thermal Phenomena); patterned surfaces with protrusions to reduce the thermal path; or direct water cooling targeted to cool the hot spots using liquid cooling (http://cooligy.com; http://www.apple.com/powermac/design.html and Bash et al. “Improving heat transfer from a flip-chip package-Company Business and Marketing”, Hewlett-Packard Journal, August 1997). All of these approaches require either complex modifications of the package lids, caps or heat sink, and or expensive water cooling with pumps, fluidic interconnects and heat exchangers.
The aforementioned methods of reducing the thermal resistance between the chip and heat sink all have one thing in common: a thermal paste/adhesive or other medium softer than the two other surfaces is always placed between the heat source and sink in order to reduce the effect of manufacturing and assembly tolerances and to simplify assembly and reworkability. The material used in these layers is usually engineered to have a low as possible thermal resistance.
Accordingly, it would be desirable to provide for reduced thermal resistance between a heat source and cooling device that is both efficacious and yet not require changes to the microprocessor fabrication process.